Pete Knobloch writes regarding his loud Duo- Art.

Since loudness is a subjective term it is difficult to tell what we are
talking about.  It would be helpful to have a graph of dynamic level vs.
vacuum level to determine whether the problem is the pneumatic system or
the piano or the room it is in.  If it is a large piano in a small room
with a low ceiling it will never be quiet enough and play with proper
dynamic control.  It may also just need voicing if the pneumatic system
is doing what it should.

Unfortunately the Duo-Art does not have a true regulating system and
therefore all variables cross-effect each other.  If there is any change
from the original factory specifications it may be difficult to get the
dynamic range correct.  Comparing the vacuum levels with a similar piano
would be a good start in determining whether the pneumatic system is
working properly.  The following points are all things to consider if the
vacuum levels are too high:

1. The zeros must be set as low as possible without dropping notes
   since the volume increases exponentially from the zero levels.
   4 wci [water column inches] for accompaniment and 4.25 to 4.5 for
   theme is a goal.

2. The spill valve adjustment is important but unfortunately original
   information is vague.  If anything is un-original -- pump capacity,
   motor speed and pulley size, muffler felt tightness, valve leakage,
   stack leakage, wind motor losses, etc. -- it can change the required
   spill valve setting.  Try setting the spill valve to produce 20 to
   25 wci at the pump at the zero level and removing the muffler felt.
   If this helps you may need to replace the felt with something dense
   enough to quiet this hiss but not dense enough to raise the volume.
   Setting the spill valve to close at level 10 only works if
   everything else is correct.

3. Springs must have correct tension and rate.  If they were replaced
   with whatever the hardware store had that looked about the same,
   this could be the problem.  Again compare them a similar piano.  You
   can hook the two springs in question together and pull them at the
   ends to see if they stretch at the same rate.

4. Since Duo-Arts depend on leakage for their regulation, anything that
   limits below the original level may increase the volume.  Were there
   cross valves that were replaced with round valves?

5. Does any weird tubing error or leakage in connector blocks cause
   un-called-for accordion closure?

6. The knife valves (accompaniment mainly) may be sticking in a strange
   way and not allow the regulators to pull them closed.  This would
   show up in a graph of playing levels.

7. Are the theme valves switching off?  The piano may be playing
   constantly on the theme regulator.

8. Is the pump motor speed and pump speed as specified in the service
   manual?  Most motors were 1150 rpm at 60 Hertz, but they made some
   real oddballs that may be running at the wrong speed with modern
   line frequency applied.  15 inch pumps should run at 120-125 rpm.,
   17 inch pumps at 110-120 rpm.  If you can, measure the speed with a
   tachometer or by counting.  If you are calculating the speed by
   motor rating and pulley sizes remember to use pitch diameter, not
   outside diameter.  This difference can be large with small pulleys.
   Standard modern belts run in a different level in the old pulleys.
   If you are using 4L belts they may be running higher causing the
   effective pitch diameter to increase thereby increasing the pump
   speed.

There are probably other things I can't think of at the moment.  It
would sure help to see a listing of your playing levels.  Is the sustain
pedal stuck on?  Is the piano action very loose?  Have the hammers
turned to stone?

-- Spencer Chase